TomGeorge:
Hi,Usually you have a metal helical gear on the output shaft of the gearbox, and a nylon or other wearable material gear on the speedo cable.
The helical gear is just about indestructible when you consider what it drives, what did you stuff up?Tom...
That's correct, however when my tranny said bye bye the differential and some other parts blew out of the casing...
I then rebuilt another one, strengthened and with a lsd differential, and a better clutch.
So now the problem is that the engine is twisting itself out of the mounts instead, but that's another story 
At this point the helical gear is eating my drives, because it's either not aligned properly or it's missing a tooth that I didn't recognize when building the new tranny...
So, instead of taking apart everything again, this could be a nice autumn/winter project, as the car is stored every winter